1. Field of the Invention
The present invention relates generally to optical fibers with core of high purity silica and fluorine doped silica cladding and optical components based on such fibers. More particularly, the present invention relates to a method of producing such optical fibers and optical components.
2. Description of Related Art
One kind of optical fiber is a step-index optical fiber. The core material of such fibers is generally classified as low or high OH silica. The optical losses of high OH fibers is mainly restricted in ultraviolet (UV) region by light scattering (Rayleigh scattering) losses, whereas the optical losses of low OH fibers are mainly restricted by absorption losses in the UV region. The absorption losses in the UV region in low OH fibers are determined by the intensive absorption bands of the intrinsic and impurity defects. Generally, such defects in glass absorb UV rays at absorption bands of 163 nanometers, 210 nanometers, 248 nanometers, 260 nanometers and 340 nanometers. High optical transmission of low OH fibers in the near infrared (NIR) region is determined by the traces of OH absorption bands. The OH content determines the low NIR transmission for the high OH fiber, e.g., fibers with OH content in the 400 to 1200 ppm range. Thus, fibers with high OH are mainly used for applications in the UV and visible (VIS) spectral regions and fibers with low OH are mainly used for applications in the VIS and NIR spectral regions.
The core glass of standard low OH preforms and fibers may typically contain up to 1000 ppm of chlorine in different forms. Because of the existence of numerous intrinsic defects and radiation centers, the low OH fibers are considered to have little or no use in the UV spectral region.
Generally, methods for improving radiation resistance and UV transmission of optical fibers are known. In such methods, the improvement is achieved (a) by increasing the concentration of dissolved hydrogen in the core with or without pre-irradiation by UV or Gamma radiation and (b) by manufacturing the glass core with special glass compositions. Such methods are usually realized using high OH fiber as the base material.